Deep Supercooling in Most Tissues of Wintering Sasa senanensis and Its Mechanism in Leaf Blade Tissues

Cold hardiness of leaf blades, leaf sheaths, culms, rhizomes, and leaf buds in wintering Sasa senanensis (Fr. et Sav.) Rehder, a dwarf bamboo, was studied paying special attention to the types of resistance mechanisms which were determined with differential thermal analysis. Coincidence of LT(25) (lethal temperature at which 25% of the tissues are injured) with the initiation temperature of LTE (low temperature exotherm) suggested that all of these tissues described above owe their cold hardiness mechanism mostly to deep supercooling. Deep supercooling in leaf blades was also substantiated with microscopic observations, suggesting that the units of supercooling were minute tissues compartmentalized by longitudinal and cross veins. It was also shown that cooling rates and storage of shoots at -5 degrees C for 1 to 5 days in the ice-inoculated state did not greatly affect the supercooling ability of leaf blades. Sasa senanensis seemed to exhibit a unique strategy against prolonged subzero temperature, and its leaves would be a good system for the study on mechanisms of deep undercooling in plants.